What is hidden in 3D image?

A terrifying explosion occurs in a gunpowder factory, and once all the mess has been cleared up, and inquiry begins.
One of the few survivors is pulled up to make a statement. "Okay Simpson," says the investigator, "you were near the scene, what happened?"
"Well, it's like this. Old Charley Higgins was in the mixing room, and I saw him take a cigarette out of his pocket and light up."
"He was smoking in the mixing room?" the investigator said in stunned horror, "How long had he been with the company?"
"About 20 years, sir"
"20 years in the company, then he goes and strikes a match in the mixing room, I'd have thought it would have been the last thing he'd have done."
"It was, sir."